1.5 Cracking Flashcards

1
Q

What is cracking?

A

The process of breaking down long chain alkanes into more useful shorter chains

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2
Q

What kind of cracking is used?

A

Thermal cracking

A variation of thermal decomposition

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3
Q

What does cracking include?

A

High heat

A catalyst

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4
Q

Describe the process of cracking

A

The long chain molecules are heated
They are vaporised
The vapour passes over a catalyst at a high temperature
The molecules are cracked on the surface of the catalyst

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5
Q

What can’t enter the reaction? Why?

A

Air

Because the oxygen reacts with the hydrogen and carbon to make H2O and CO2

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6
Q

What is the name given to the other hydrocarbon made in cracking?

A

Alkenes

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7
Q

What is the formula for an alkene?

A

C(n)+H(2n)

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8
Q

What do alkenes have that alkanes don’t?

A

At least one double bond

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9
Q

What does the double bond make the alkene?

A

Unsaturated

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10
Q

What bonds do alkenes have?

A

4 carbon bonds
1 hydrogen bond

At least one double bond between carbons

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11
Q

What is the chemical test for alkenes?

A

They will discolour bromine water from orange to colourless because the double bond reacts with the bromine water

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12
Q

Name the first 4 alkenes

A

Ethene
Propene
Butene
Pentene

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13
Q

What is polymerisation?

A

Many monomers join together to make a polymer

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14
Q

What is an alkene called in the plastics industry?

A

A monomer

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15
Q

What conditions are needed for polymerisation?

A

High heat
High pressure
A catalyst

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16
Q

What changes in the many monomers to make polymers?

A

The double bond breaks

17
Q

What does each of the monomers: ethene, propene and styrene become in polymerisation?

A

Polyethene
Polypropene
Polystyrene

18
Q

What chemical is added to polymers to make them into plastic?

A

Plasticisers

19
Q

What are the problems with plastic?

A

Non-biodegradable
Non-renewable
Burning them produces CO2

20
Q

What is a thermoplastic?

A

A plastic that can be heated and shaped into a new shape as it is melted down

21
Q

What is a thermoset?

A

A plastic that will not change on heating

22
Q

Example of a thermoset?

23
Q

What makes a thermoset and a thermoplastic different?

A

The strength of the bonds between polymers

24
Q

What are biodegradable plastics made from?

A

Corn starch?

25
What is the advantage of biodegradable plastics?
Break down more easily | Renewable
26
What two ways can ethanol be produced?
Fermentation | Hydration of ethene
27
How do you get ethanol in fermentation?
Sugar -> ethanol + carbon dioxide
28
What are the advantages of fermentation?
Renewable Uses little energy Large quantities produced
29
What are the disadvantages of fermentation?
Increases food prices Slow process Ethanol needs to be purified in distillation
31
How do you get ethanol from hydration of ethene?
Ethene + steam (+catalyst) -> ethanol
32
What are the advantages of hydration of ethene?
Fast process Continuous Very pure ethanol
33
What are the disadvantages of hydration of ethene?
Non-renewable Uses a lot of energy High temperatures are needed